1. Field of the Invention
The present invention relates to a system and methods used to determine pressure measurements within an endotracheal tube for use in calculation of parameters in lung mechanics and for use in determining the patency of the endotracheal tube. More specifically, the present invention is related to a system and methods for maintaining the patency of at least one pressure line in fluid communication with a major lumen of an endotracheal tube to ensure the viability of pressure measurements from the pressure line for subsequent use in calculation of parameters in lung mechanics and for use in determining the patency of the endotracheal tube, particularly for patients who are connected to a ventilator.
2. Background Art
Endotracheal pressure measurements are needed to calculate lung mechanics, for example, the calculation of work of breathing, lung compliance, and airway breathing. Such pressure measurements may also be used to assist in controlling the breathing support supplied by a ventilator, for example, the use of pressure support ventilation, demand flow ventilation and tracheal pressure control ventilation. These pressure measurements are particularly needed in patient""s undergoing surgery and/or in a condition requiring connection to a ventilator.
Ventilators are commonly employed to assist the patient in breathing and typically include two main lines which are independently connected from the ventilator to separate branched arms from a Y-tube junction. A connector is inserted into the open stem of the Y-tube for further connection with an endotracheal tube or tracheostomy tube extending from the trachea of the patient. The main lines, the Y-tube and the connector form a breathing circuit to provide the necessary breathing support required by the condition of the patient. Airway pressure, which is the air pressure within the endotracheal tube proximate the proximal end of the endotracheal tube and may be used in such calculation of lung mechanics, is typically measured at the connection between the endotracheal tube and the breathing circuit. More particularly, it is typically measured between the endotracheal tube and the Y-tube of the breathing circuit.
At an appropriate pressure support ventilation level, the total work of breathing of the patient is shared between the ventilator and the patient. For the ventilator to perform a portion of the work of breathing, an appropriate level of pressure support ventilation must be preselected. To set the ventilator properly and relieve the patient""s work of breathing, tracheal pressure must be accurately measured to calculate the imposed resistive work of breathing. The tracheal pressure is the air pressure within the endotracheal tube proximate the distal end of the endotracheal tube, i.e., proximate the trachea of the patient. During demand-flow spontaneous ventilation and tracheal pressure control ventilation, the patient must perform some desired portion of the work of breathing and generally must create a negative pressure to initiate a breath. Using tracheal pressure or a combination of tracheal pressure and the airway pressure measured at the connection between the endotracheal tube and the breathing circuit as the triggering pressure decreases the response time in initiating the breath and the patient""s work of breathing.
Tracheal pressure can be measured by placing a catheter down the endotracheal tube or by using an endotracheal tube having a secondary lumen in the endotracheal tube wall, which is open at the distal end of the endotracheal tube. The catheter and the secondary lumen are subject to kinking and mucosal blockage. Tracheal pressure can be significantly lower than airway pressure and the pressure difference can change if the pressure lines that are in fluid communication with the distal and/or proximal ends of the endotracheal tube become obstructed or partially obstructed with water, or mucous, or kinked, any of which can shut off or limit the flow of fluid through the respective pressure line. Obstructions within the pressure lines may result in erroneous tracheal and/or airway pressure readings. Without the correct pressure measurements of tracheal pressure and/or airway pressure, the derived data based on the incorrect pressure measurements are predisposed to be in error, which may result in insufficient ventilation of the patient.
Additionally, if the endotracheal tube itself becomes obstructed with water or mucous or kinked, the flow of air delivered to the patient can be limited or shut off, which would insufficiently ventilate the lungs of the patient. Patency of the endotracheal tube may be determined by comparing the pressure of the fluid at the distal end of the endotracheal tube, i.e., the tracheal pressure, to the pressure of the fluid at the proximal end of the endotracheal tube, i.e., the airway pressure. However, the measurement of these pressures may be adversely affected by water or mucosal blockages within the respective pressure lines.
The present invention relates to a pressure monitoring system for an endotracheal tube. The endotracheal tube has an open distal end, an opposing open proximal end, and a major lumen extending within the tube from the proximal end to the distal end. The distal end of the endotracheal tube is in fluid communication with a trachea of a patient.
The pressure monitoring system has at least one pressure line, a purging subsystem, and a pressure monitoring subsystem. Each pressure line is in fluid communication with the major lumen of the endotracheal tube. The purging subsystem is in fluid communication with at least one of the pressure lines. The pressure monitoring subsystem is in operative communication with each pressure line and has means to monitor the pressure of fluid within each respective pressure line.
For each pressure line in that is in fluid communication with the purging subsystem, the pressure monitoring subsystem may generate a response signal in response to a determined pressure within the pressure line which indicates that the pressure line is obstructed. In response to the response signal generated by the pressure monitoring subsystem, the purging subsystem supplies a pressurized fluid to the pressure line with which the purging subsystem is in fluid communication. This pressurized fluid clears the obstruction from the pressure line so that accurate pressure readings may be obtained from the pressure line. After a predetermined time period subsequent to the generation of the response signal, the pressure monitoring subsystem terminates the supply of the pressurized fluid to the pressure line.
In one embodiment, the pressure lines may include a first pressure line that is in fluid communication with the distal end of the endotracheal tube so that a tracheal pressure may be measured. Because of the high probability of blockage due to its proximity to the trachea and lungs of the patient, this first pressure line may also be in fluid communication with the purging subsystem so that the patency of the first pressure line may be maintained. Alternatively, in another embodiment, the pressure lines may include a second pressure line that is in fluid communication with the proximal end of the endotracheal tube. This second pressure line enables the measurement of airway pressure. The second pressure line may also be in fluid communication with the purging subsystem.